Magnetically actuated switching devices



Jan. 16, 1968 GOULD ET AL 3,364,449

MAGNETICALLY ACTUATED SWITCHING DEVICES 3 Sheets-Sheet 1 Filed Dec. 18,1963 O O O O HLB GOULD WVENTORZV 0H. WEN/V), JR

/ ATTORNEY Jan. 16, 1968 GOULD ET AL 3,364,449

MAGNETICALLY ACTUATED SWITCHING DEVICES Filed Dec. 18. 1963 3heets-Sheet 2 FIG. 2

TVP/CAL DC HVSTERES/S LOOP REMENDUR 24,000 5(GAUS5) MAX 0 BF 20,000 fiiI --|2,000 a 8000 I I I --4000 I HG 100 so so 40 20 20 40 so so I00H(0E/P5TED5) Jan. 16, 1968 H. B. GOULD ET AL 3,364,449

MAGNETICALLY ACTUATED SWITCHING DEVICES Filed Dec. 18, 1963 5Sheets-Sheet 5 :,JL .1 37 i Q.

a/ as 3,364,445 MAGNETHCALLY ACTUATED SWITCHING DEVICES Harold L. B.Gould, Kinnelon Borough, and Daniel H. Wenny, .lr., Morris Township,Morris County, N.J., assignors to Bell Telephone Laboratories,Incorporated, New York, N.Y., a corporation of New York Filed Dec. 18,1963, Ser. No. 331,434 1 Claim. (Cl. 335-153) This invention relates toa class of electromagnetically controlled switching devices employingremanently magnetic members, and more particularly to such devicesemploying alloys of vanadium, cobalt, and iron in such remanent members.

In the Bell System Technical Journal for January 1960, at pages 1 etseq, there is described a class of switching devices designatedferreeds. These devices, characterized by the provision of scaledmetallic contacts while being controllable at electronic speeds, are sodesigned that they can be left switched without holding power beingrequired. They have control times in the microsecond range and arecapable of selection by the use of coincident currents.

The prototype device, as described in that publication, constitutes amagnetically hard ferrite member in combination with a magnetic reedswitch utilizing two soft magnetic reeds. The reed switch and ferritemember are so arranged as to form a series magnetic circuit,magnetization of the ferrite member by passage of current through anenveloping coil bringing about closure of the reeds. Ferritecompositions are chosen so as to have a sufiicient remanent field tomaintain closure after current flow is discontinued.

While ferrite compositions utilized in the devices described in thepublication have appropriate coercivity, remanence, and squareness topermit efiicient operation, subsequent development work revealed astrong temperature dependence of coercivity, either requiring closetemperature control or the use of greater drive currents, most seriousin coincident current operation.

In accordance with this invention, it has been discovered that a seriesof vanadium-cobalt-iron alloys represented by the exemplary composition3.5% vanadium, 48% cobalt, 48% iron, and 0.5% manganese, when processedin accordance with a specific range of conditions here set forth,manifests substantial temperature insensitivity of coercivity over abroad range of operating temperatures while being possessed ofcoercivity, remanence, and squareness values well adapted to theoperation of ferreed devices. Persons familiar with this developmenthave already adopted the term Remendur as encompassing the compositionsprocessed in accordance with the conditions set forth herein. The termRemendur, as used herein, refers to the entire range of compositions andprocessing conditions herein described as suitably adapted to theferreed devices of this invention.

In the course of this description, the use of the term ferreed hasreference to the prototype devices as originally described in the BellSystem Technical Journal. As applied to this description, such devicesutilize not ferrite elements but metallic alloy elements of thecompositions set forth. In addition to overcoming the most seriousdrawback of the ferrite element, i.e. temperature dependence ofcoercivity, the use of these metallic elements has obvious structuraladvantages, e.g. ease of fabrication, shock resistance, etc. A furthercharacteristic, a thermal coefficient of expansion approximating that ofa commercially used sealing alloy, makes possible a new class of ferreeddevices in which the reeds are themselves contates Patent structed ofthe remanent material, so eliminating the need for any external magneticstructures.

Compositions of concern for the uses described herein are known to beuseful for their magnetic properties. For example, the nominalcomposition in its soft state is known as Supermendur, which manifestsone of the highest permeability values of the known alloys. A partiallyworked material of this compositional range is dis closed in UnitedStates Patent 2,519,277, issued Aug. 15, 1950, to E. A. Nesbitt et al.The device which is the subject of this patent is a self-biasedmagnetostrictive sonic generator, use being made of the remanent andcoercive characteristics of the alloy.

It has been noted that the devices of this invention utilize the nominalcomposition 3.5% vanadium, 48% cobalt, 48% iron and 0.5 manganese. Themanganese inclusion serves the well-known function of minimizing thedeleterious effect of any sulfur inclusion. The amount of manganese isnot critical and can be eliminated entirely if precautions are taken toavoid sulfur inclusion. While amounts as great as 1 percent or more maybe used, onehalf of 1 percent usually sufiices, with no furtheradvantage accruing with greater inclusion. It is well known that any ofseveral other elements including cerium, magnesium, beryllium, andcalcium may be utilized.

Vanadium is included to improve cold-workability of the resultant alloy.The major ingredients, cobalt and iron, are, of course, mainlyresponsible for the magnetic properties of the alloy. A preferred rangeon a 100 part basis for the total of these two ingredients is from partscobalt to parts cobalt, with a broader range extending from 40 to partsof this ingredient. It is seen that greater freedom exists forincreasing cobalt inclusion, and it is this ingredient which is chieflyresponsible for increased coercivity and for workability. In general,increasing cobalt content results in decreasing saturation andremanence, however such values being adequate for any of the devicesherein at levels far above the maximum inclusion indicated. Fullnessratio, and this discussion is largely in terms of this quantity, BH /B,H(where BH is the second quadrant product of flux in gauss and appliedfield in oersteds yielding the largest numerical value, and B and H arethe values of flux and applied field in the same units for zero fieldand zero flux, respectively), increases for increasing cobalt from avalue of about 62 percent at 40 parts to about percent for 50 parts. Theratio decreases slightly for greater cobalt inclusion and is at a valueof about 75 percent for 75 parts. For the uses herein a value of 0.60 isconsidered a preferred minimum.

Vanadium content is critical. Its range extends from 1 percent up toabout 5 percent. Its minimumvalue for optimum properties is somewhatdependent on cobalt content, with the low value indicated correspondingwith the greatest cobalt inclusion. Minimum vanadium content is about 2percent for equal amounts of cobalt and iron and about 1 percent at 75parts cobalt. Vanadium inclusion improves workability, increasesresistivity, improves fullness ratio, increases magnetic saturation, andincreases coercivity. Increasing vanadium above the maximum indicatedresults in a decrease in remanent magnetization. Remendur compositionswithin the ranges discussed, and when processed according to theteaching herein, are magnetically isotropic up to a vanadium content ofabout 3 /2 percent. While suitable device properties may be obtained inthe anisotropic compositionscontained herein, isotropy may facilitatethe adaptation of these materials to a variety of devices. Ease offabrication of certain 70 ferreed elements requires bending in thedirection of cold-working and the utilization of magnetic properties ina normal direction. While it is possible to develop desired propertiesin such a normal direction, in an anisotropic material such may requirea different processing schedule than that used for the processing ofmaterial in which magnetic properties parallel to the direction ofworking are of consequence. Accordingly, it is expedient to maintainvanadium content at a maximum value of 3.5 percent. This value istherefore considered to be a preferred maximum.

While composition may be varied over relatively long ranges, at leastwith regard to the major ingredients, the magnetic properties of thefinal material are extremely sensitive to processing conditions. It is'an absolute requirement that the final processing step be a partialanneal following a cold reduction. While there should be no treatmentintermediate final cold working and anneal such as to affect magneticproperties, it is at this stage that the parts are punched and shaped.Where reference is made to directly following working by final anneal itshould be so construed. The cold reduction, which may be effected byrolling, drawing, swaging, etc., must be at least 60 percent inaccordance with the equation where Z equals cold reduction in percent, Aequals original cross section area, and A equals final cross sectionarea. A preferred figure is 90 percent on the same basis such reductionresulting in a fullness ratio of at least 6-5 percent.

The partial anneal may be carried out over the temperature range of from400 C. to 675 C. Optimum time of anneal ranges from about one-half hourat 675 C. to about twenty hours at 400 C. Some increase in heating timeis permissible, maximum times ranging from 1 hour to 25 hours, the lowervalue again corresponding with the higher temperature of 675 C. Minimumvalues may range from hour to 15 hours, the lower value correspondingwith the higher temperature. Minimum heating time is somewhat dependenton the cross-section of the body being treated. While this is not aprimary consideration for the sections adaptable to the devices herein,which do not generally exceed 0.05 inch, with appreciably largersections, heating time should be sufficient to heat the inner portion ofthe body. Some of the specific examples herein are concerned withelements which were heat treated for from one to three hours at atemperature of from 550 to 575 C., and this range of Z Percent ColdReduction conditions is therefore to be considered optimum.

Partial anneal as well as any process (lead) anneals are desirablycarried out in a protective atmosphere over the temperature range downto 350 C. to prevent oxidation of vanadium although air is permissiblefor processing of thicker sections (60 mils and up). Suitableatmospheres are hydrogen, forming gas, argon, helium, nitrogen, etc.

Some of the physical properties of Remendur are briefly set forth. Theprocessing conditions discussed are for the two terminal steps. Previoushistory has little effect and may consist of the usual sequentialcold-working and dead anneals as applied to many materials in the courseof producing the fine wire ribbon or rod structures suitable for use inswitching elements of the type discussed herein.

Workability.-The alloy is quite hard mechanically and in the annealedstate has a Rockwell hardness of C-20 while possessing a persistentmalleability and ductility. It has been rolled to sheet and foil as thinas .2 mil, drawn to wire 1 mil in diameter, and been flattened toribbons ranging from .5 mil to 8 mils in thickness and mils to 65 milsin width.

Temperature coefficient of expansion values average 10.26 times perdegree C. over the temperature range 30 C. to 550 C. This value is aboutthe same as that of the commercial 52 percent nickel-iron glass sealingalloy now used in dry reed and mercury switches. In addition, the alloyseals readily to glass.

Plating characteristics.--Remendur has been plated with up to .5 milthick layers of copper, silver and gold, which platings adhere well withor without a bonding heat treatment and resist cold reduction.

Some of the magnetic properties are set forth:

Permanent magnet properties include coercive forces up to about 60oersteds and residual inductions (remanent fields) up to about 21,500gauss.

Temperature Lstability.As discussed in conjunction with FIG. 1, thecoercive force is stable over a temperature range of from 60 F. to F.

Description of the invention is expedited by reference to the drawings,in which:

FIG. 1, on coordinates of apparent coercive force in oersteds on theordinate and temperature in degrees C. on the abscissa, is a plotshowing the temperature sensitivity of coercive force for two samples,one of Remendur and the other a typical ferrite;

FIG. 2 is a typical D-C hysteresis loop for a Remendur sample plotted onthe usual ordinates of B in gauss on the ordinate and H in oersteds onthe abscissa;

FIG. 3 is a perspective view of one ferrced configuration utilizingRemendur elements;

FIG. 4 is a perspective view of a different type of ferreed alsoutilizing a Remendur element; and

FIG. 5 is a front elevational view, partly in section, of a ferreedstructure in which a reed is itself constructed of Remendur.

Referring again to FIG. 1, curve 1 shows the variation in coercive forcewith temperature for an alloy of the invention, while curve 2 shows thevariation in coercive force with temperature for a ferrite compositionotherwise possessed of the requisite magnetic characteristics for use ina ferreed device. Comparison of the curves readily indicates therelative temperature insensitivity of coercivity of the Remendur sample.

FIG. 2 shows a conventional hysteresis loop for an alloy of theinvention having the nominal composition 3.5% vanadium, 48% cobalt, 48%iron, and 0.5% manganese.

The significance of the fullness factor, BH /B fi is seen from thisfigure. The point in the second quadrant corresponding with the maximumvalue of the product BH occurs at the knee 10 of the curve. This iscompared with the product B the remanent field, taken at point 11, andthe coercive force H at 12. This is a more meaningful term than theusual squareness ratio ordinarily considered as the ratio B to the fluxvalue at saturation B (taken at point 13). The fullness factor for thehysteresis loop shown is 71.5%, which compares favorably to the minimumvalue of 50% which is usually specified for devices of the naturediscussed herein.

The device of FIG. 3, the prototype of which is described in UnitedStates Patent 3,075,059, issued Jan. 22, 1963, is sometimes called theseries ferreed. The device depicted includes a pair of magnetizablereeds 21 and 22 constructed of a soft magnetic material enclosed withina glass envelope 24. Overlapping portions of reeds 21 and 22 serve ascontact areas 23, which are normally separated. Surrounding envelope 24there is a split or C sleeve 25 of an alloy herein. Disposed about thesleeve, in' the vicinity of the contact areas 23 of the reeds 21 and 22,is a shunt plate 26 of a permeable soft magnetic material.

Wound about the sleeve 25 on both sides of the shunt plate 26 are twosets of windings 27 27 and 28 28 the pair of 27 and 28 windingsterminating at A, A and B, B respectively. Each of the windings 27 and28 has twice the number of turns of each of the windings 27 and 28 topermit differential operation, as discussed in United States Patent3,075,059. The A windings are interconnected at terminal A while the Bwindings are interconnected at terminal B A complete description of theoperation of the device of FIG. 3 or of the other devices herein is notappropriately included in this disclosure and may be obtained byreference to the Blaha patent, supra, or to the Bell System TechnicalJournal reference. Very briefly, switch closure is accomplished sopassing current through the windings creating a magnetic path such thatflux closure is accomplished through the reeds 21 and 22 at contactareas 23. The remanent field to maintain closure must, of course, be ofsuificient strength to overcome the stiffness of the reeds. Thiscondition obtains in the device of FIG. 3 when pulses applied at A and Bare such as to produce the same direction of magnetization through theportions of sleeve 25 on either side of shunt 26. Reversing thedirection of magnetization of either of the two halves of sleeve 25results in a flux path through shunt 26, so eliminating any substantialflow of flux through either of the reeds.

In the device of FIG. 4, two bistable, remanently magnetic membersconstructed of an alloy herein control two reed switches. The deviceshown is one type of parallel ferreed.

This device is described in United States Patent 2,995,- 637, issued onAug. 8, 1961.

The device of FIG. 4 includes a pair of Remendur rods and 31, suspendedbetween a pair of soft magnetic disks 32 and 33. Also suspended betweenthe disks 32 and 33, adjacent to the rods 30 and 31, are two reedswitches 34 having individual terminals 35 which protrude through andare electrically insulated from the disks 32 and 33. Reed switches 34may be identical to that enclosed within tube 24 of FIG. 3. A winding 36encircles both of the rods 30 and 31. A winding 37 is shown wound aboutthe rod 31 alone.

The arrangement shown provides for a coincident drive to operate theswitches 34, but achieves release by current in a single winding.Initially, to prepare the device for use, Remendur rods 30 and 31 aremagnetically saturated in the same direction (either up or down in thedevice as depicted) by passage of a current through winding 36. Sincethe flux associated with either of the Remendur rods 30 or 31 is opposedby that of the other, the flux of both rods seeks a path through reedswitches 34-, so accomplishing closure. For the particular embodimentdepicted, the remanent magnetization state of rod 30 is now establishedand will be unaffected by future operation.

In normal operation, switches 34 are released by application of acurrent to winding 37 with a direction and magnitude such that theremanent magnetization of rod 31 is reversed. This establishes a fluxpattern, with the flux in opposite directions in the two rods 30 and 31,and with these two rods now defining a closed magnetic circuit, sobypassing switch 34.

Closure is accomplished by coincident drive currents appliedsimultaneously to windings 36 and 37. Each of these currents isinsufficient to reverse the magnetization of rod 31, but the magnetizingforce of both coincident currents reverses this state, so restoring theinitial flux pattern for closing switches 34. Since only one winding 36is associated with rod 30, and since the current applied to 36 is, initself, insufiicient to reverse the remanent field, this rod remainsunaffected.

The device of FIG. 5 is illustrative of those embodiments in which atleast one reed is itself constructed of a remanently magnetic material,as described herein. This figure depicts a reed switch having a glassenvelope 41, with terminals 4-2. A Remendur reed 43 is attached to theleft-hand terminal 42. A second reed 44, which may be constructed of ahighly permeable soft magnetic material or of an alloy of thisinvention, is attached to the right-hand terminal 42 so that its freeend overlaps the free end of reed 43 to form a contact pair at 49. Alsoattached to the right-hand terminal 412 is a permanent magnet 45 havinga magnetic polarity, as shown. A coil 7 5 Fullness ratio, ltH /B -H 46is wound about the envelope 41 on the portion enclosing the reed 43.

Operation of the device is similar to that of those described above,with coil 46 biased in such manner that the magnetization direction ofreed 43 corresponds with that of reed 14 (induced by permanent magnet45) and closure is accomplished. Reversing the direction ofmagnetization in reed 43 results in two separate flux paths, the oneincluding reed 43, the other, reed 44, in which condition the naturalstiffness of the reeds results in release.

The following examples relate to the preparation of a range of alloycompositions in accordance with the processing conditions hereindescribed.

Example 1 A melt was prepared of the following materials:

Kilograms Electrolytic cob-alt 1.536

Electrolytic iron 1.375 Ferro-vanadium (0.112 kilogram vanadium, 0.161

kilogram iron) 0:273

Electrolytic manganese .016

On reaching a temperature of 1550" C. the melt was held 2 minutes toinsure a thorough mixing and solution of the ingredients and was thenpoured into a mold and solidified to make an ingot. The ingot was heatedto a temperature of about 1250 C. for hot rolling to a thickness of0.060 inch strip or hot swaging to inch diameter rod. The hot rollingwas accomplished in 14 passes with nominal reductions of 0.050 inch perpass and reheating as required. Hot swaging was done in 20 passes withreductions of 0.025 inch per pass. The hot worked strip and rod wereprepared for cold working by heating to 900 C. and quenching in icebrine. They were then sufiiciently ductile to be cold worked. The stripwas finished at 6 mils thickness (an area reduction of and the wire at22 mils with anneals at A; and inch.

The cold worked alloy was then heat-treated at 1103": 27 F. (5991-15 C.)for 1201-10 minutes in :an inert atmosphere such as forming gas, or inan atmosphere of hydrogen. The furnace was allowed to cool to 662-572 F.(350-300 C.) and the atmosphere was then changed to air (the air servingsolely to blue the alloy and improve corrosion resistance). Thistemperature and atmosphere were maintained for 1015 minutes.

In the heat treated condition, the composition had magneticcharacteristics as follows:

Residual induction, B (gausses) 18,200 Coercive force, H (oersteds) 38Squareness ratio, B /B 0.92 Fullness ratio, 13l I /1Eh l5' 0.75

All measurements were D-C measurements at a magnetizing force of H:1001-5 oersteds.

Example 2 After processing, as indicated, the composition had thefollowing magnetic characteristics:

Residual induction B, gauss 17,200

Coercive force, H oersteds '48 Squareness ratio, B /B 0.90

Example 3 The procedure of Example 1 was repeated, however utilizing thefollowing amounts of the indicated materials:

After processing, as indicated, the composition had the followingmagnetic characteristics:

Residual induction B gauss 21,500 Coercive force, H oersteds 25Squareness ratio, B /B 0.95 Fullness ratio, BH /B H .85

Example 4 The procedure of Example 1 was repeated, however utilizing thefollowing amounts of the indicated materials:

Kilograms Cobalt 2.240 Iron .677

Ferro-vanadium-(0.112 kilograms vanadium, 0.156

kilogram iron) .267 Manganese .016

After processing, as indicated, the composition had the followingmagnetic characteristics:

Residual induction, B gauss 15,000 Coercive force, H oersteds 50Squareness ratio, B /B 96 Fullness ratio, BH /B H 71 The invention hasbeen described in terms of a limited number of illustrative embodiments.As is well known to those skilled in the art, the devices depictedconstitute 7 but a limited portion of a vast class of switching devicesin which closure is maintained by means of the remanent magnetic fieldof one or more associated elements. Most of the description has been interms of a particular class of such devices which have come to be knownas ferreeds by reason of the fact that the remanently magnetic materialwas a ferrite. It is clear from this description that the remanentlymagnetic materials herein are suitably adapted to all such devices, aswell as to any other design in which a remanent field of sutlicientstrength to overcome the stiffness or other force accomplishing releaseis of sufficient strength to maintain closure without application of aholding current. The invention is considered to reside in the discoverythat the alloys herein are possessed of temperature insensitivity ofcoercivity, square hysteresis loop, high residual induction, and othersuch properties as to make them suitable for use in this class ofdevices.

The magnetic alloy has been discussed in terms of the nominalcomposition vanadium-iron-cobalt. It is well known that small amounts ofvarious elements including, for example, chromium, zirconium, titanium,nickel, etc. may be incorporated desirably in such alloys for thepurpose of altering such properties as switching time, resistivity, etc.Such additional ingredients are considered to be within the scope ofthis invention, both as described and claimed.

What is claimed is:

1. Device comprising a magnetic circuit including a pair of normallyopen switch contacts of a magnetic material together with at least twoseparately magnetizable body portions, each of said portions having amagnetic fullness ratio of at least 50 percent and each of said portionsconsisting essentially of an alloy containing from 40 to 75 parts byweight cobalt, 25 to parts by weight iron, and 1 to 5 parts by weightvanadium, said body portions having been produced by a series ofprocessing steps terminating in a cold reduction of at least 60 percent,followed by a partial anneal during which anneal the said body portionsare maintained at a temperature of from about 400 to 675 C. for a timeperiod of from onequarter to 25 hours, the shorter times correspondingwith the higher temperature, the said body portions being magneticallybistable, the arrangement being such that closure is accomplished bymagnetization of both portions in such direction that the lowestreluctance magnetic circuit includes the two portions as well as thesaid switch contacts, the remanent field of the said portions being ofsulficient strength to overcome the normal force maintaining the saidswitch contacts open so that closure is maintained, and in which releaseis accomplished by magnetization of one portion in a direction oppositeto that resulting in closure.

References Cited UNITED STATES PATENTS 1,862,255 6/1932 White et' al 1232,190,667 2/1940 Kelsall et al 335102 2,298,225 10/1942 Nesbitt 1481022,519,277 8/1950 Nesbitt et a1. 317201 2,995,637 8/1961 Feiner et al200-87 3,059,075 10/1962 Peek 200'87 3,075,059 1/1963 Blaha et a1.200-87 3,128,418 4/1964 Zupa 20087 OTHER REFERENCES Feiner et al.: TheFerreed, a New Switching Device, The Bell System Technical Journal, v01.XXXIX, No. 1, January 1960, pp. 1-30, pp. 12-14 relied on.

BERNARD A. GILHEANY, Primary Examiner.

R. N. ENVALL, 1a., Assistant Examiner.

1. DEVICE COMPRISING A MAGNETIC CIRCUIT INCLUDING A PAIR OF NORMALLYOPEN SWITCH CONTACTS OF A MAGNETIC MATERIAL TOGETHER WITH AT LEAST TWOSEPARATELY MAGNETIZABLE BODY PORTIONS, EACH OF SAID PORTIONS HAVING AMAGNETIC FULLNESS RATIO OF AT LEAST 50 PERCENT AND EACH OF SAID PORTIONSCONSISTING ESSENTIALLY OF AN ALLOY CONTAINING FROM 40 TO 75 PARTS BYWEIGHT COBALT, 25 TO 60 PARTS BY WEIGHT IRON, AND 1 TO 5 PARTS BY WEIGHTVANADIUM, SAID BODY PORTIONS HAVING BEEN PRODUCED BY A SERIES OFPROCESSING STEPS TERMINATING IN A COLD REDUCTION OF AT LEAST 60 PERCENT,FOLLOWED BY A PARTIAL ANNEAL DURING WHICH ANNEAL THE SAID BODY PORTIONSARE MAINTAINED AT A TEMPERATURE OF FROM ABOUT 400 TO 675* C. FOR A TIMERPERIOD OF FROM ONEQUARTER TO 25 HOURS, THE SHORTER TIMES CORRESPONDINGWITH THE HIGHER TEMPERATURE, THE SAID BODY PORTIONS BEING MAGNETICALLYBISTABLE, THE ARRANGEMENT BEING SUCH THAT CLOSURE IS ACCOMPLISHED BYMAGNETIZATION OF BOTH PORTIONS IN SUCH DIRECTION THAT THE LOWESTRELUCTANCE MAGNETIC CIRCUIT INCLUDES THE TWO PORTIONS AS WELL AS THESAID SWITCH CONTACTS, THE REMANENT FIELD OF THE SAID PORTIONS BEING OFSUFFICIENT STRENGTH TO OVERCOME THE NORMAL FORCE MAINTAINING THE SAIDSWITCH CONTACTS OPEN SO THAT CLOSURE IS MAINTAINED, AND IN WHICH RELEASEIS ACCOMPLISHED BY MAGNETIZATION OF ONE PORTION IN A DIRECTION OPPOSITETO THE RESULTING IN CLOSURE.